Speed reduction gear assembly

ABSTRACT

A speed reduction gear assembly wherein a large speed reduction is realized from input to output using a minimum of four gears. The input is coaxial with the output. The large gear reduction is a result of the effective rolling center of one of the gears being located at a predeterminable radial point other than on the pitch diameter of the gear it is driving. Alternative embodiments are provided which allow, through the use of additional gears, the transfer of a large amount of torque and permit the rotational output to be taken on the input side of the gear assembly.

United States Patent [191 Boor [ 1 June 26, 1973 [73] Assignee:Fairfield Manufacturing Co., v

Lafayette, Ind.

[22] Filed: Aug. 19, 1971 211 Appl. No.: 172,998

[52] US. Cl. 74/801 3,120,764 2/1964 Berlinger, Jr. et a] 74/801 PrimaryExaminer-Arthur T. McKeon Attorney-Verne A. Trask et al.

57 ABSTRACT A speed reduction gear assembly wherein a large speedreduction is realized from input to output using a minimum of fourgears. The input is coaxial with the output. The large gear reduction isa result of the effective rolling center of one of the gears beinglocated at a predeterminable radial point other than on the pitchdiameter of the gear it is driving. Alternative embodiments are providedwhich allow, through the use of additional gears, the transfer of alarge amount of torque and permit the rotational output to be taken onthe input side of the gear assembly.

5 Claims, 6 Drawing Figures PATENTEUmzs ms 3.741 041 Fig. 3

PAIENIED JUNZSISH v 3 74L041 SHEEI 3 BF 3 1 SPEED REDUCTION GEARASSEMBLY BACKGROUND OF THE INVENTION The present invention relates to acompact gear assembly which effects a large speed reduction with aminimal number of gears. Heretofore, nominal speed reductions have beenobtained using a compound planetary gear train or coupled singularplanetary gear trains. The singular planetary, gear configuration orsingle epicyclic train consists of a sun pinion gear, a planet gear, andan internallytoothed ring gear. The planet gear is in mesh with the sungear and the internally toothed ring gear. The sun gear is rotated .todrive the planet gear which in turn causes the internal ring gear torotate. If the internal ring gear is held in position, the planet gearnot only rotates but orbits the sun gear within the stationary internalring gear.

A double planetray gear train has a planet gear with its axis rotatablyconnected to a spider which is rotated by the orbital movement of theplanet gear about a sun 1 gear. A second sun gear is connected to thespider and the coaxial input and output shafts.

A compound planetary gear comprises a sun gear, an internally toothedring gear, two planet gears mounted on the same axis and-an output'gear.The first planet gear orbits the sun gear within and in mesh with theinternal ring gear. The second planet gear is rotated by the first andin turn drives the output gear.

Each stage of the multi-stage planetary can effect a reduction inthepractical range of 3:1 to 8:1. Therefore for a two stage planetary trainthe largest reduction would be in-the range of 60 or 70:1. This wouldrequire a minimum of six gears. More planet gears would have to be addedto effect a proportional increase in torque transfer capacity. Theaddition of planets would not alter the speed reduction. Conventionallya minimum of three planet gears per stage would be used for nominaltorque transfer. This would require a total of ten gears for a maximumreduction of about 70:1.

The compound gear assemblies utilize cluster gears mounted on the planetgear shafts to drive a subsequent stage as the three or more planetgears in the first stage and their shafts are rotated. Cluster gears aremultiple gears cut on a single axis under the requirement that the twosets of teeth be properly aligned with each other. Cluster gearsnecessitate meticulous mounting techniques for equal load. distributionbetween the three planets.

It is therefore an object of this invention to provide a compact geartrain capable of a large speed reduction with a minimum number of gearsrequiring no alignment between gears and to effect this reduction with alarge and concurrent torque transfer.

SUMMARY OF 'THE INVENTION In accordance with the invention, a large gearreduction is obtained using a minimum of four gears. Two of the gears, adrive pinion and a planet idler pinion may be rotatably mounted in afixed relationship with one another in a rotating carrier. The carriermay be mounted on an input shaft. The drive pinion and the planet idlerpinion are positioned so as to mesh with each other. The planet idlerpinion also meshes with an internally toothed ring gear which is mountedin a fixed position. The drive pinion, on the other hand, also mesheswith an output gear mounted on the output shaft which is coaxial withthe input shaft and the internally toothed ring gear.

In operation, the input shaft rotates the pinion carrier. The planetidler pinion, being engaged with the internal ring gear, rotates aboutits own axis and orbits about the center of the internal ring gear dueto the rotating carrier. The planet idler pinion in turn rotates ordrives the drive pinion which turns the output gear. It has been foundthat the planet idler pinion has an effective rolling center which islocated on the pitch diameter of the internally toothed ring gear. Thedrive pinion, being held in the carrier in a fixed relationship with theplanet idler pinion and driven thereby, also rotates about an effectiverolling center located on the pitch diameter of the internal ring gear.The output gear, which preferably has a pitch diameter less than that oftheinternal ring gear, is driven by the drive pinion. It has been foundthat the speed of the output gear is related to this difference in pitchdiameter between the output gear and the internal ring gear. The speedreduction for this gear configuration has been found to be equal to thenumber of teeth in the output gear divided by the difference between thenumber of teeth in the output gear and thenumber of teeth in theinternal ring gear. The number of teeth .in the drive pinion and theplanet idler pinion do not affect the ratio. For example, with aninternal ring gear having 67 teeth and an output gear having 66 teeththe speed reduction ration would be 66 to l. I 1

Alternatively, a sun gear may be mounted on the input shaft in mesh withthe planet idler pinion. In this case, the planet idler and drive pinioncarrier is rotated by the orbiting of the planet idler pinion about thesun gear within the-internally toothed ring gear. Again, the

planet idler pinion and the drive pinion mesh with each other and rotateon a moving effective rolling center which is on the pitch diameter ofthe internal ring gear. The speed reduction has now been increased, bythe addition of a single gear, on the order of 3 to 8 times. The speedreduction obtained has been found to be the quantity obtained by addingthe number of teeth in the sun gear to the number of teeth in theinternal ring gear divided by the number of teeth in the sun gear, timesthe quantity found by taking the number of teeth in the output geardivided by the number of teeth in the internal ring gear minus thenumber of teeth in the output gear. It may be seen that by substitutingappropriate tooth numbers in this equation that the gear ratio availableis quite high, especially since only a total of five gears are used.

Multiple planet idler pinions may be added to both of the aboveconfigurations to increase the torque transfer capabilities of theassembly. In' such case, each planet idler pinion would have a drivepinion in mesh with it. The speed reduction ratio would not be changed.

A larger gear reduction may be obtained by constructing a multiple stageassembly, either withor without an input pinion. In this instance, thedrive pinion reduction ratio may be determined by multiplying the speedreduction ratios of each of the stages together.

While the preferred embodiment uses a fixed internally toothed ring gearand a rotatable output gear, it will be understood that the gear drivenby the drive pinion could be fixed and the output taken from theinternal ring gear which would be permitted to rotate. In addition, andalso within the scope of my invention, while the input and output shaftsare coaxial, they need not be on opposite ends of the gear train but maybe on the same end or side.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustratethe invention and, by way of example, show preferred embodiments of theinvention. In such drawings:

FIG. 1 is an axial section of a gear assembly embodying the invention;

FIG. 2 is a diagrammatic showing of the embodiment of FIG. 1

FIG. 3 is an axial section of an alternative embodiment of the assemblyof FIG. 1;

. FIG. 4 is an axial section of another alternative embodiment of theassembly of FIG. 1;

FIG. 5 is an end view of the assembly shown in FIG. 4; and ,7

FIG. 6 is a multiple stage gear assembly embodying the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An apparatus embodyingmy invention is shown in FIG. 1, and generally comprises a housing 10with front and rear panels 12 and 14. These two panels are held togetheras by an elongated sleeve 16, bolt 18 and nut 19. The housing 10supports and partially encloses a reduction gear assembly 20. The lowerportion of the housing 10 may be sealed and partially filled with an oilor other lubricant for the assembly 20 to pass through for lubricationpurposes. A bushing 22 in the righthand panel 12, as shown in FIG. 1,rotatably supports an input shaft 24 for the gear assembly 20. A flange26 is formed on, or attached to, the input shaft 24 within the housing10. A planet idler pinion 28 is rotatably mounted by means of a bushing30 in a fixed axial position on the flange 26, as by a bolt 32. Theplanet idler pinion 28 meshes with an internally toothed ring gear 34which is mounted in fixed relationship with the right plate 12 by a bolt36 and spacer 38. The planet idler pinion 28 extends beyond the face ofthe internal ring gear 34 and meshes with a drive pinion 40. This drivepinion 40 is rotatably mounted by means of a bushing 42 in a pinioncarrier 44. The carrier 44 is also connected, by means of a bolt 46, tothe flange 26 on the input shaft 24.

The drive pinion 40 extends beyond the face of the planet pinion 28 andmeshes with an output gear 48. This gear 48 is cut on or attached to anoutput shaft 50 which extends through and is supported in the left plate14 of the housing 10 by a bushing or bearing block 52. An output devicesuch as a sprocket gear 54 may be attached as by a key 56 to the outputshaft 50.

In operation, the input shaft 24 may be rotated at a high speed as by anelectric motor. The rotating shaft 24 rotates the flange 26. The axis ofthe planet idler pinion 28 being carried on this flange 26 is therebyrotated in a circular path as is the axis of the drive pinion 40 beingcarried in the pinion carrier 44 also attached to this flange 26. Theplanet idler pinion 28 also rotates about its own axis due toits meshingengagement with the internal ring gear 34. The drive pinion 40 rotatesabout its own'axis due to its meshing engagement with the planet idlerpinion 28. The drive pinion 40 meshes with and turns the output gear 48as it is orbited about that gear by the pinion carrier 44.

The speed or gear reduction obtained from the reduction gear assemblyabove described has been found to be the number attained by dividing thenumber of teeth in the output gear 48 by the quantity found by takingthe number of teeth in the internal ring gear 44 minus the number ofteethin the output gear 48. For example, if the internal ring gear has67 teeth and the output gear has 66 teeth, the speed reduction would be66 dividedby 67 minus 66 or 66:1.

The large gear reduction obtained with this configuration which utilizesonly four gears may be explained with reference to the diagrammaticalshowing of FIG. 2. In the diagram, an input shaft'60 turns in acounterclockwise direction. A planet idler pinion 62 is connected to theinput shaft by a connecting member 64. This member 64 corresponds to theflange 26 on the input shaft 24 in .FIG. 1. A second connecting member66 connects the axis of a drive pinion 68 in a fixed relationship tothat of the planet idler pinion 62. This corresponds, in FIG. 1, to thepinion carrier 44. If the input shaft 60 in FIG. 2 is turned in acounterclockwise direction, the axes of the drive pinion 68 and planetidler pinion 62 also travel in a counterclockwise circular path. Theangular relationship between the member 66 connecting the two pinionsand the member 64 connecting the planet pinion and the input shaft isfixed and does not change during rotation. The planet idler pinion 62and drive pinion 68 also rotate about their axes due to their engagementwith each other and with the internal ring gear 70 and output gear 72respectively. It has been found that the planet idler pinion 62 has aneflective rolling center during rotation on the pitch diameter of theinternal ring gear 70. Furthermore, the drive pinion also rotates aboutan effective rolling centerwhich is also located on the pitch diameterof the'intemal ring gear 70 due to the fixed relationship of the drivepinion to the planet idler pinionand since the two pinions rotate at thesame speed. The drive pinion 68 is also in mesh with the output gear 72.The effective rolling center of the drive pinion is, however, located onthe ring gear which is larger in pitch diameter than the output gear. Itis the offsetting of the effective rolling center of the drive pinion 68from the pitch diameter of the output gear .72 which incurs a largespeed reduction.

By way of explanation, if the ring gear and the planet idler pinion wereremoved, the axis of the drive pinion 68 were fixed in position and thepinion 68 rotated in mesh with theoutput gear 72, the speed reductionwould be equal to the number of teeth or pitch diameter of the otuputgear divided by the number of teeth or pitch diameter of the drivepinion. The effective rolling center of the drive pinion in this casewould be located at the center of the drive pinion.

However, if the drive pinion were rotated and its axis free to move, thedrive pinion would become a planetary pinion and rotate about its ownaxis as well as orbit about the output gear. In this instance, theeffective rolling center of the drive pinion would be on the pitchdiameter of the output gear and the speed reduction would be infinite.By reinstating the planet idler pinion and internal ring gear and usingthem to locate the effective rolling center of the drive pinion at aradial posi-' tion onthe drive pinion somewhere between the center ofthe drive pinion and the extremities of the pitch diameter of the outputgear many different desired gear reductions may be obtained.

Another embodiment of my invention is illustrated in FIG. 3. An inputshaft 74 extends through and is rotatably supported in a housing mmeber76 on the input side of the apparatus. An input pinion 78 is mounted onand keyed to the internal end of the input shaft 74. A planet idlerpinion gear 80 is rotatably mounted on a bushing 82 in a pinion carrier84. The planet idler pinion 80 meshes with the input pinion 78 and aninternally toothed ring gear 86. The internal ring gear 86 is held inposition by a spacer 90 and a bolt 92. A drive pinion 94 is rotatablymounted by means of a bushing 96 in the pinion carrier 84. The idlerplanet pinion 80 also meshes with the drive pinion 94. The position ofthe drive pinion 94 with respect to the planet idler pinion 80 is fixedby their mountings in the carrier 84. This position is determined by thepitch diameter of an output gear 98. The drive pinion 94 must bepositioned within the carrier so that it meshes both the planet idlerpinion and the output gear 98.

The shaft 100 carrying the output gear extends through and is supportedin a panel 102 on the output side of the apparatus by a bushing 104.This panel 102 and the panel 76 on the input side are held together asby a plurality of bolts and sleeves 106.

In operation, the input shaft 74 is rotated to drive the input pinion78. This pinion rotates the planet idler pinion 80. The planet idlerpinion 80, in addition to rotating about its own axis, orbits within theinternal ring gear 86. The drivepinion 94'is rotarily driven by theplanet idler pinion 80 and also orbits therewith due to the fixedrelationship of the two pinions within the pinion carrier 84. The drivepinion 94, as it rotates and orbits, drives the output gear 98 whichturns the output shaft 100. The speed reduction obtainablewith thisassembly is equal to the sum of the number of teeth in the internal ringgear 86 and the number of teeth in the input pinion 78 all divided bythe number of teeth in the input pinion 78' and then'the quotient takentimes the number of teeth in the output gear 98 divided by thedifference in the number. of teeth between the internal ring gear 86 andthe output gear 98.

In an apparatus where more torque transfer is required, multiple idlerplanet and drive pinion pairs may be added. The input pinion, the pinioncarrier and the internal ring gear should then be permitted to moveslightly with respect to one another so that they can seek theirowncenter. For. the ring gear, the slight movement required can beeffected by loosely mounting it on pins instead of the illustrated bolts92. This is done because the planet idler pinion gears cannot each becut exactly the same. Each planet idler pinion may also have two drivepinions associated therewith to effect an even larger torque transfer tothe output gear.

A gear assembly is illustrated in FIGS. 4 and 5 which permits the inputand output to be taken coaxially on the same side of the apparatus. Inthis configuration, the input is supplied to a collar 110 which isconnected on an input shaft 112 by a set screw 114. The input shaft isunsupported except for the collar 110 and extends almost the completewidth of the housing 116 and is culminated in an inputpinion 118. Thispinion 118 is in mesh with three planet idler pinions 120 which arerotatably mounted on bushings 122 in a pinion carrier, 124. The planetidlers mesh with an internally toothed ring gear 126 and a like numberof drive pinions 128 which, like the planet idler pinions, are rotatablyniounted on bushings 130 in the pinion carrier 124. The input pinion 118is rotated by the input collar 110 to rotate the planet idler pinions120 which cause them to orbit about the input pinion within the internalring gear 126. The drive pinions 128, in fixed relationship with theplanet idler pinions within the pinion carrier 124, are rotated by theplanet idler pinions and orbit therewith to drive the output gear 132which is connected by a set screw 134 to an output collar 136. The speedreduction ratio of this apparatus is determined by the same formula asthe apparatus of FIG. 3. Again, the number of planet idler pinions anddrive pinions may be increased, e.g. to four or five, to effect an 7increase in the torque tranfer capabilities of the assembly. I

A multiple stage gear assembly embodying my invention is shown in FIG.6. This device comprises a housing which is comprised of a panel on theinput side 142 and a panel on the output side 144 held together as by abolt and spacer sleeve arrangement 146. Input is provided by an inputshaft 148 which is mounted in a bushing 150 in the input side panel 142.The input shaft 148 is connected to or formed as part of a circularflange 152 within the housing 140. A planet idler pinion 154 isrotatably mounted on a bushing 156 and mounted by means of a bolt 158 tothis circular flange 152. The planet idler-pinion 154 is in mesh with aninternal ring gear 160 which is connected to the input panel 142. It isalso in mesh with a drive pinion 162 which is rotatably mounted on abushing 164 in a pinion carrier 166. This pinion carrier is alsoconnected, by means of a bolt 168, to the circular flange 152 on theinput shaft 148. As the' input shaft 148 turns, it

carries with it the planet idler pinion 154 and the drive pinion carrier166 in a fixed relationship. The planet idler pinion l54 rotates as itsteeth mesh with those of the internal ring gear 160 and in turn drivesthe drive pinion 162.

- The drive pinion 162, as it rotates, also meshes with another gear 170which constitutes the output gear for the first stage. A second planetidler pinion 172 is connected by a bolt 174 and bushing 176 to the firststage output gear 170. The nature of this connection mandates that thesecond planet idler pinion gear 172 orbit about the center of rotationof the first stage output gear 170 while being free to rotate about itsown axis due to its meshing engagement with a second internally toothedring gear 178. This second internal ring gear is rigidly fixed to thegear housing 146.

A second pinion carrier 180 is also connected to the first stage outputgear 170, as by a bolt 171. A second drive pinion 182 is rotatablymounted on a bushing 184 in this carrier 180. The carrier maintains anexact relationship between the positions of the second drive pinion 182and the second planet idler pinion 172. The drive pinion 182 extendspast the face of the planet idler pinion 172 and meshes wtih an outputgear 186 which is connected to or formed on the end of an output shaft188. The output shaft 188 is mounted in the output panel 144 by means ofa bushing or bearing 190. A sprocket wheel 192 may be mounted on theoutput shaft 188 to effect the rotational output.

The speed reduction ratio of the gear assemblies hereinbefore describedmay be altered greatly by changing only the output gear. For example,using the apparatus shown in FIG. 1, if the internal ring gear has 63teeth and the output gear has 62 teeth, the reduction ratio would be62/(63-62) or 62:1. The ratio may be reduced to 2:1 by changing the 62tooth output gear with one having 42 teeth. The number of teeth in theplanet idler pinion and the drive pinion do not enter the calculationsso there is no compatibility needed between the number of teeth theyhave and the number the internal ring gear and output gear each has.

I claim:

1. A gear assembly which comprises, a frame for supporting the assembly,rotational input means rotatably supported by said frame; an internallytoothed ring gear fixed to said frame, an idler pinion in mesh with saidinternally toothed ring gear; coupling means for operatively couplingsaid rotational input means to said idler pinion; a pinion carrier forrotatably mounting said idler pinion therein; a drive pinion rotatablymounted in said pinion carrier in mesh with said idler pinion, and anoutput gear coaxial with said input means and in mesh with said drivepinion, whereby said idler pinion is rotated by said rotational inputmeans to effect an orbiting of said carrier, and thereby said idlerpinion and said drive pinion, within said ring gear due to the mesh- 8ing engagement of said idler pinion and said ring gear, said orbiting ofsaid drive pinion and said meshing engagement of said drive pinion andsaid idler pinion being effective for altering the rolling center ofsaid drive pinion to incur a speed reduction between said rotationalinput means and said output gear.

2. A gear assembly as claimed in claim 1, wherein said coupling meansincludes a flange secured to said rotational input means and rotatablemounting means supported thereon for rotatably mounting said idlerpinion to said flange.

3. A gear assembly as claimed in claim 1, wherein said coupling meansincludes an input pinion mounted on said rotational input means and inmesh with said idler pinion.

4. A gear assembly as claimed in claim 3, wherein a second idler pinionis rotatably mounted in said pinion carrier in mesh with said internallytoothed ring gear and said input pinion, and a second drive pinion isrotatably mounted in said pinion carrier in a fixed axial position withrespect to said second idler pinion and in mesh therewith, said seconddrive pinion also being in mesh with said output gear.

5. A gear assembly as claimed in claim 4 wherein said internally toothedring gear is loosely secured to said frame.

t k I t

1. A gear assembly which comprises, a frame for supporting the assembly,rotational input means rotatably supported by said frame; an internallytoothed ring gear fixed to said frame, an idler pinion in mesh with saidinternally toothed ring gear; coupling means for operatively couplingsaid rotational input means to said idler pinion; a pinion carrier forrotatably mounting said idler pinion therein; a drive pinion rotatablymounted in said pinion carrier in mesh with said idler pinion, and anoutput gear coaxial with said input means and in mesh with said drivepinion, whereby said idler pinion is rotated by said rotational inputmeans to effect an orbiting of said carrier, and thereby said idlerpinion and said drive pinion, within said ring gear due to the meshingengagement of said idler pinion and said ring gear, said orbiting ofsaid drive pinion and said meshing engagement of said drive pinion andsaid idler pinion being effective for altering the rolling center ofsaid drive pinion to incur a speed reduction between said rotationalinput means and said output gear.
 2. A gear assembly as claimed in claim1, wherein said coupling means includes a flange secured to saidrotational inpuT means and rotatable mounting means supported thereonfor rotatably mounting said idler pinion to said flange.
 3. A gearassembly as claimed in claim 1, wherein said coupling means includes aninput pinion mounted on said rotational input means and in mesh withsaid idler pinion.
 4. A gear assembly as claimed in claim 3, wherein asecond idler pinion is rotatably mounted in said pinion carrier in meshwith said internally toothed ring gear and said input pinion, and asecond drive pinion is rotatably mounted in said pinion carrier in afixed axial position with respect to said second idler pinion and inmesh therewith, said second drive pinion also being in mesh with saidoutput gear.
 5. A gear assembly as claimed in claim 4 wherein saidinternally toothed ring gear is loosely secured to said frame.